1. Field of the Invention
The present invention relates generally to a call admission system and method in a mobile communication system, and in particular, to a system and method of determining whether to admit a new or handover call in a mobile communication system.
2. Description of the Related Art
A mobile communication system has been developed to provide voice and data service, ensuring user mobility. Thus an MS (Mobile Station) exchanges data with a BTS (Base Transceiver Station) on radio channels. In the mobile communication system, authentication of the mobile station is performed upon initiation of or request for a call.
The configuration of the mobile communication system will be described with reference to FIG. 1. FIG. 1 illustrates connections between nodes in a typical mobile communication system.
Referring to FIG. 1, an MS 1 with mobility conducts voice or data communications with BTSs (BTS-a to BTS-n) 10-a to 10-n on radio channels. The BTSs 10-a to 10-n are controlled by a BSC (Base Station Controller) 20 and connected to each other over a network such as a WAN (Wide Area Network). The BSC 20 is connected to the Internet/PSTN (Public Switched Telephone Network)/PSDN (Public Switched Data Network) 60 through a gateway/mobile switching center (GW/MSC) 30, for call connection. The GW 30 is a logical name and is commonly referred to as a Packet Data Service Node (PDSN), Access Gateway (AGW), or Media Gateway (MGW).
A profile server 40 stores information in user profiles such as the Identifier (ID) of each subscriber and authentication parameter. A user profile is illustrated in Table 1 below.
TABLE 1Subscriber IDAuthentication ParameterAdditional Information
In Table 1, the user profile comprises a Subscriber ID that identifies a subscriber, an Authentication Parameter for authenticating a subscriber, and Additional Information. The profile server 40 is a logical entity. Physically, it can be integrated into the GW/MSC 30.
FIG. 2 is a diagram illustrating a signal flow for an operation of admitting or rejecting an incoming call in the mobile communication system of FIG. 1.
When an originating node requests a call setup to the MS 1, the call setup request is connected to the mobile communication system. That is, a system to which the originating node belongs transmits a call setup request signal to the GW/MSC 30. The GW/MSC 30 then transmits a Call-Establishment-Req message to the BSC 20 in step 100. The BSC 20 transmits a User-Profile-Req message to the profile server 40 in step 102. In step 104, the profile server 40 generates a User-Profile-Res message by searching a user profile as illustrated in Table 1 and transmits it to the BSC 20. The User-Profile-Res message is constructed from either a part of or the whole of the contents of Table 1.
In step 106, the BSC 20 performs a CAC (Call Admission Control) operation to determine resource availability. If it is determined from the result of the resource availability check that the call cannot be admitted, the BSC 20 transmits a Call-Establishment-Rej message to the GW/MSC 30 in step 108. If the call is admitted, the BSC 20 transmits a Call-Establishment-Req message to the BTS 10-a in step 110. The BTS 10-a then performs a CAC operation to determine whether to admit the call in step 112. If the call is admitted, the BTS 10-a transmits a Call-Accept-Res message to the BSC 20 in step 114-a. If the call cannot be accepted, the BTS 10-a transmits a Call-Establishment-Rej message to the BSC 20 in step 114-b. 
Upon receipt of the Call-Accept-Res message from the BTS 10-a, the BSC 20 forwards the Call-Accept-Res message to the GW/MSC 30 in step 116-a. However, upon receipt of the Call-Establishment-Rej message from the BTS 10-a, the BSC 20 forwards the Call-Establishment-Rej message to the GW/MSC 30 in step 116-b. In the above procedure, a call is either admitted or rejected during the call setup stage.
However, the CAC operations in the BSC 20 and the BTS 10-a involves only resource availability, and excludes the Quality of Service (QoS) of a call from consideration. No problems arise if a voice call, instant message, or simple Internet service is provided. Yet, one of the clear trends these days is the provision of various services including Video on Demand (VoD), Music on Demand (MoD), and Wireless ISP (W-ISP) to satisfy growing user demand for these services. These services often require real-time transmission. Thus, while a call is connected, a large amount of data must be transmitted continuously or for a Selected time. If a call is assigned by determining the availability of resources, it may occur that a user-requested data rate is not supported. If the BTS or BSC assigns a call requiring high-speed data transmission in the same manner as a voice service requiring low-speed data transmission, a required data rate cannot be ensured. Therefore, QoS is notguaranteed in the conventional call setup.